HP StorageWorks External Storage XP user guide (December 2005)

12 External Storage XP for the XP10000/XP12000
NOTE: With the exception of MSA, a host can directly access external disk array volumes that have not
been mapped as local disk array volumes.
Figure 1 External Storage XP concept
Figure 1 illustrates a connection between a local disk array and an external disk array interconnected
using External Storage XP software and fibre channel hardware. In this figure, the external disk array is
connected to the external port of the local disk array via a switch (or hub) using a Fibre Channel interface.
External is a kind of XP10000/XP12000 port attribute used for External Storage XP. In the figure, external
LUs are mapped as local disk array VDEVs and LDEVs and, consequently as an LU.
NOTE: The phrases “mapped as an internal LU” and “mapped as an internal LDEV” should be interpreted
to mean that the external LU is specifically mapped into the XP10000/XP12000 as a unique VDEV
(Virtual Device), which is then associated with an XP10000/XP12000 CU:LDEV (Control Unit:Logical
Device), which is then typically associated with a unique host port/LU combination. Since an
XP10000/XP12000 LU number is only unique within the name space of a host port (for example, CL1-A),
references to “XP LU” should be interpreted as references to either the unique port/LUN combination or the
unique CU:LDEV combination.
NOTE: Do not access any external storage volume that is mapped as an External Storage XP volume from
a host connected directly to the external disk array. Also, do not access an External Storage XP mapped
external array volume using the external disk array’s functions (for example, local replication). After
mapping an external disk volume as a local XP10000/XP12000 volume, access the mapped external
disk volume only via the local XP10000/XP12000 disk array.
Alternate paths
When you map an external LU as an internal XP LDEV, a path (called a mapped path) is set from the
internal XP LDEV to the external LU. In addition to the original path, you can set additional paths to the
external LU, called alternate paths.